Concerns over the environmental consequences of burning fossil fuels have led to an increasing use of renewable energy generated from sources such as solar and wind. The intermittent and varied nature of such renewable energy sources, however, has made it difficult to fully integrate these energy sources into electrical power grids and distribution networks. A solution to this problem has been to employ large-scale electrical energy storage (EES) systems, which systems are widely considered to be an effective approach to improve the reliability, power quality, and economy of renewable energy derived from solar or wind sources.
Among the most promising large-scale EES technologies are redox flow batteries (RFBs). RFBs are special electrochemical systems that can repeatedly store and convert megawatt-hours (MWhs) of electrical energy to chemical energy and chemical energy back to electrical energy when needed.
In simplified terms, an electrochemical cell is a device capable of either deriving electrical energy from chemical reactions, or facilitating chemical reactions through the introduction of electrical energy. In general, an electrochemical cell includes two half-cells, each having an electrolyte. The two half-cells may use the same electrolyte, or they may use different electrolytes. With the introduction of electrical energy, species from one half-cell lose electrons (oxidation) to their electrode while species from the other half-cell gain electrons (reduction) from their electrode. Multiple electrochemical cells electrically connected together in series within a common housing are generally referred to as an electrochemical “stack”.
A redox (reduction/oxidation) flow battery (RFB) is a special type of electrochemical system in which electrolyte containing one or more dissolved electro-active species flows through electrochemical cells. A common RFB electrochemical cell configuration includes two opposing electrodes separated by an ion exchange membrane or other separator, and two circulating electrolyte solutions, referred to as the “anolyte” and “catholyte”. The energy conversion between electrical energy and chemical potential occurs instantly at the electrodes when the liquid electrolyte begins to flow through the cells.
One problem associated with RFBs is the creation and existence of shunt currents in and between electrochemical stacks during operation. Because of the conductivity of the liquid electrolytes and a non-zero electrical field potential gradient, shunt currents can flow between individual cells and cell stacks by traveling through pathways of conductive liquid electrolytes. The presence of shunt currents can reduce each stack's overall electrical storage and discharge capacity and decrease the energy efficiency of the overall system. Thus, it is desirable to reduce and/or eliminate shunt current losses within flow electrochemical energy systems while also minimizing mechanical pumping losses in those systems.
Accordingly, there is a need for new and improved flowing electrolyte electrochemical energy systems and related methods for fluid flow. The present disclosure fulfills these needs and provides for further related advantages.